Method of manufacturing tinplate



June 2s, 1963 M. D. STONE 3,095,361

METHOD OF MANUFACTURING TINPLATE Filed Feb. 27, 1961 'l v2a INVENTOR. Q)me/5 a. .sra/v5 ArraQ/vey 3,095,361 Patented June 25, 1963 snee3,095,361 METHOD OF MANUFACTURING TINPLATE Morris D. Stone, Pittsburgh,Pa., assignor to United Engineering and Foundry Company, Pittsburgh,Pa., a cerporation of Pennsylvania Filed Feb. 27, 1961, Ser. No. 91,7083 Claims. (Cl. Zim- 28) This invention relates to a method of producingvery thin tinplate characterized by a high production capacity andcapable of producing tinplate at a substantial saving in manufacturingcosts over known methods and wherein the tinplate will have improvedmetallurgical characteristics.

This economic and metallurgical advancement in the production oftinplate is realized by practicing a method in which the parent strip isreduced to an ultra-thin gauge thereby affording a considerable savingsin cost of material, equipment and labor as may be required forproducing the tinplate, as well as a marked reduction in scrap losses,while, at the same time, yielding a product having improved hardness andstrength characteristics.

In view of the fact that normal gauge tinplate, which falls within theranges .007 to .011 inch, is not economically suitable for all phases ofthe container market, the ability of tinplate to maintain and tocontinue to improve its position in this market depends to anappreciable extent on whether ultra-thin tinplate can be produced moreeconomically. One lof the major problems confronting the economicalmanufacture of very thin tinplate has to do with whether the tinplatewill have the requisite physical properties to enable it to serve itsintended purpose. Two other major problems have to do with theadditional equipment necessary to produce such tinplate and theconsiderable scrap losses incident thereto. These scrap losses arebrought labout as :a result of the thin strip being damaged during themany processing, handling and transferring steps which are involved inthe production of the tinplate. Because of the magnitude of theseproblems, it has been questioned by some skilled in the art whether verythin tinplate can be economically produced.

In order to better understand the uniqueness and novelty of the presentinvention, an understanding of the present-day commercial attempts atproducing very thin tinplate is believed necessary. At present, thereare but two such procedures for making available in limited amountsultra-thin tinplate lfor use in the manufacture of containers.

One procedure is to utilize the `ordinary processing equipment employedto produce normal gauge tinplate, which consists of reducing the hotrolled and pickled strip in a tandem cold reduction rolling mill wherethe strip is reduced immediately to its ultra-thin gauge, i.e., to anorder of .0045" thick. This `operation is followed by a continuousannealing process, wherein the ultra-thin strip is cleaned and annealedto a soft metallurgical condition. Thereafter, the strip, which is notonly very thin but also very soft, both of which factors being conduciveto high scrap losses, is transferred to a skin-pass rolling mill forfurther processing. This operation is designed primarily to develop thedesired mechanical properties, along with achieving a smoother andflatter strip surface. The strip, however, retains a considerable degreeof softness after the skin-.pass operation.

Subsequent to this skin-pass operation, the ultra-thin strip istransferred for the third time to an electrolytic tinning line. In thetinning line, the strip is rst cleaned, pickled and tinned, after whichit is passed through reilowing, passivating or chemical treatment andoiling zones. In this procedure, it is to be appreciated that it isnecessary to repeatedly handle, transfer and process the strip in itsultra-thin and soft condition; in which connection when cognizance istaken of the intricacies of the equipment that performs this manner ofprocessing of the very thin strip, it will really be understood whygreat scrap losses are involved. Moreover, in this procedure it has beenfound that the strip could only be rolled to the thin desired gauges byoverloading the conventional 5-stand tandem cold mill, or by using a6-stand mill, or alternately by a second succeeding separate rollingstep. In this connection, it is to be pointed out that the maximumhardness that has been found practical to achieve in this method hasfallen within the range of -6 (T-30 Rockwell of 67 to 73).

With respect to the second procedure currently being used in an attemptto produce ultra-thin tinplate, in order to minimize the necessity ofhandling, transferring and processing the strip in its ultra-thin andsoft condition, the procedure is essentially as follows:

The -hot rolled strip in this case is reduced to approximateiy the orderof .020 inch thicker than in the case of the previous explained method,ie., approximately of the order of .100 inch thick. The hot rolled andpickled strip is transferred to a tandem cold reducing mill where thestrip is reduced to a thickness of the order of .009 inch, that is,approximately double its final desired thickness. After the coldreduction operation, the strip is transferred in its still relativelythick gauge to an annealing line, where it is cleaned and annealed inthe usual manner. From the annealing line, the strip, still in itsrelatively thick but now soft state, may then be processed in askin-passing mill, although, in some cases, this step may not beincluded. The strip is then transferred to a thinning line, where it iscleaned, pickled, tinned, reowed, passivated or chemically treated andoiled. After tinning, the strip is then reduced about 50% in a secondcold reduction mill to the iinal desired ultrathin gauge and having thedesired hardness. The degrees of hardnesses that are known to beobtained in this method have been lwithin the range of T-7 (T-30Rockwell of 7l to 78). After the rolling of the tinned strip, it istransferred in its ultra-thin condition to a fourth process line and toits sixth independent processing step where it is cleaned andpassivated, and sometimes reflowed for the second time.

In this second procedure, while it has the advantage that the thinproduct in its soft condition is involved in less handling than in thefirst procedure, it will be appreciated that to obtain this advantage asubstantial increase in equipment and labor force is necessary.Moreover, in view of the `fact that the tinned strip is subjected to arolling operation in which the surface of the strip may become marred,it is necessary to perform a second reilow operation as well as achemical treatment and a second cleaning operation. it goes withoutsaying that such an overall process results in increased cost ofmanufacturing the tinplate.

it is the principal object of the present invention to provide a methodof manufacturing tinplate that will be ultra-thin and of low cost, thatwill keep to a minimum the scrap losses incident to the productionthereof, that will require no additional equipment and labor force overthe first method described above and Still considerably less withrespect to the second aforementioned method, and yet will have theadvantage `of a high pardoduction capacity which will not involveadditional cleaning, reflowing or chemical 4treating operations toproduce tinplate having Ia maximum of hardness and strength as impartedby cold rolling.

This object and the other novel features of the present invention willbe more fully appreciated when the fol- 'a a lowing description thereofis read in light of the drawing in which;

FIG.`1 illustrates diagrammatically and in sequence the novel steps ofthe present invention.

As will be apparent to those skilled in the art, the various processingunits illustrated in FIG. l and described hereinafter employed in theherein disclosed rnethod are in themselves well-known elements in themanufacture of steel strip as exemplified in The Making, Shaping andTreating of Steel, United States Steel, 7th edition.

With reference t FIG. l there is shown the last mill stand of a hotstrip rolling mill 11 wherein the hot strip is reduced in thickness andfollowing which it is coiled on a mandrel 12. In order to realize thefull advantages of the present invention it is recommended that thestrip be reduced in the hot rolling imill to a gauge within the range of.080 to .110 inch thick. For the purpose of describing the presentinvention, it will be assumed that the thickness of the strip issuingfrom the hot mill is of the order of .100 inch. The hot rolled strip, inthe form of a coil, is transferred from the mandrel 12 to a picklingline 13 in which it is, in the usual manner, placed on a pay-off reel14, joined to the end of a previous strip and fed through the picklingzones, after which it is coiled again on a wind-up reel 15. Of course,the strip during the pickling operation is still in a very thickcondition, Ii.e., as previously mentioned .100 inch, so that there willbe experienced no scrap losses such as would result if very thin stripwere being pickled.

From the pickling line, the pickled strip in coiled form, is transferredto a tandem cold reduction mill 16 where the coil is placed on a pay-offreel 17, fed through each of the five, or as shown in phantom six,stands of the mill and then wound on a tension reel 18. Acconding to theteachings of the present invention, the strip will be reduced in thecold reduction mill to a thickness within the range of .006 to .012inch. For the purpose of this description, it will be assumed that thethickness of the strip issuing from the cold mill 16 is of the order of.009 inch. This thickness represents approximately double the desiredfinal thickness of the product. In this condition, it is to be observedthat the strip will be still relatively thick and by reason of therolling operation very hard. In view of the fact that the stripsthickness -is approximately twice as great as its ultimate desiredgauge, the handling, transferring and the immediate subsequentprocessing thereof will lbe done without experiencing the considerablescrap losses that are inherent in handling very thin material,

After the cold reduction mill operation, the relatively thick hardstrip, in coil form, is transferred to an annealing line 19 where it isplaced on a pay-off reel 21 and the leading end joined to the trailingend of `a previous istrip, and fed through the annealing line. As iscustomary, the strip will be cleaned before being annealed lafter whichit will pass through the annealing zone and be coiled on a windup rcel22. It is to be appreciated that at this stage of the operation thestrip, as it leaves the annealing line, will be very soft, but at thesame time it will have a substantial thickness, and in view of this factin the further handling, transferring and processing thereof, scraplosses will be minimized.

Following the :annealing operation, the strip -in coiled form, istransferred to :a second cold reduction mill 23 which may consist ofeither one or two or more stands, a second stand being shown in phantomin the drawing. In this operation the strip, in coiled form, is adaptedto be placed on a pay-off reel 24, fed through the mill and wound upon atension reel 25. As pointed out above, the strip when it is transferred.from the annealing line and during the time it is being handled at theentry side of the second reduction mill 23 will be in a soft condition,but at the same time it will be relatively thick, hence minimizing scraplosses during this phase of the operation. According to the teaching ofthe present invention, the strip is adapted to be giVeIl its finalreduction to its ultra-thin form in the reduction mill Z3 in which thethickness should be within the range of .003 to .006 inch. In thisregard, it is important to point out that in order to achieve the fulladvantage of this invention, the reduction taken in the -rnill 23 shouldbe of the order of from 30 to 60 percent. For the purpose of thedescription of the present invention, it will be assumed that the finalthickness of the strip will be of the order of .0045 inch, which willrepresent a 50 percent reduction. As mentioned previously, a substantialsavings in the overall cost of producing the tinplate is thus realizedin reducing the thickness of the strip to Such an extent. It is one ofthe features of this invention to provide a method wherein suchtinplate, resulting from the practice thereof, will have thischaracteristic. In this connection, it is to be appreciated that notonly is the mill 23 employed at this particular stage of the operationto reduce the strip to its final thickness prior to tinning, but just asimportant and of equal significance is the fact that the reduction takenwithin the previously mentioned range will impart a substantial hardnessto the strip and, in addition, will improve its strength qualities. Itis ya feature of the invention herein disclosed that the strip will begiven a hardness of the order of T-6 to T-S (T-3O Rockwell of 67 to 83)and that this hardness will be achieved primarily by rolling. It will beappreciated that this degree of hardness will enable the tinplate to beused for the intended purpose, notwithstanding its extreme thinness.

After the second cold reduction operation the strip, in coil form, istransferred in its very thin but very hard condition to an electrolyticthinning line 26 where it is placed on a pay-olf reel 27, joined to thetrailing end of a previous strip, and fed through the line, after whichit will be coiled upon a windup reel 28. This electrolytic tinning lineincorporates the usual equipment adapted to electro-clean, pickle, tin,reow, passivate and oil the strip. It is a feature of this invention toperform all rolling of the strip prior to the tinning operation therebyavoiding the possibility of marring the tinned surfaces. To accomplishthis object, the strip, according to the present invention, Will bepresented to the thinning line in its nal very thin gauge. However,since by employing the method of the present invention, the strip willhave a substantial hardness and improved strength qualities obtained bycold rolling of the strip and as a result scrap losses Iwill beminimized in the further transferring, handling and processing of thestrip.

In summarizing the advantages of the present invention over the priorprocedures for attempting to produce tinplate more economically, it willbe appreciated that the present invention provides a method wherein theresulting tinplate is made very thin with a substantial reduction in thematerial cost and in the practice of which substantially all of thetransferring, handling and processing of the strip are performed, while4the strip is still in its soft thick condition. Furthermore, when thestrip is in its very thin condition, which is only for a small fractionof the overall processing and handling time, this strip is maintainedvery hard so that a considerable reduction in the scrap losses over theentire processing operation is effected. In addition, the strip not onlywill be characterized by a substantial hardness and improved strengthqualities, which are achieved by rolling, but the strip after tinningwill not he subjected to any rolling, thereby resulting in an overalladvantage that not only is the product economically produced but it isproduced on a line having a very high capacity.

In accordance with the provisions of the patent statutes, I haveexplained the principle and operation of my invention and haveillustrated and described what I consider to represent the bestembodiment thereof. However, I desire to have it understood that withinthe scope of the appended claims, the invention may be practicedotherwise than as specifically illustrated and described.

I claim:

1. In a method of producing tinplate characterized by a high degree ofhardness suitable for use in the manufacture of containers, the stepsincluding:

cold reducing the strip to a thickness of at least .006

inch and thicker;

annealing such strip;

cold reducing the annealed strip by an amount of at least 3() percentand greater yto impart to the strip a hardness of at least T-5,

and electrolytically tinning the strip in its thin hard condition.

2. In a method of producing tinplate suitable for use in the manufactureof containers in a minimum number of processing steps and in a mannerthat scrap losses will be substantially reduced and the strip will becharacterized by a high degree of hardness achieved by rolling, thesteps including:

reducing this strip in a hot rolling mill to a thickness between thelower and upper limits of .080 to .110 inch, respectively;

further reducing the cold strip in a cold rolling mill to a thicknessbetween the lower and upper limits of .006 to .012 inch, respectively;

annealing said strip as cold reduced;

cold reducing the annealed strip by an amount between the lower andupper limits of 30 to 60 percent, respectively to impart to the strip ahardness between the lower and upper limits of T-6 to T-S, respectively,

and continuously electrolytically tinning the strip in the thin hardcondition. 3. In a method of producing very thin tinplate characterizedby the fact that when the strip is in a metallurgically soft condition,it is maintained relatively thick, and when in its very thin conditionthe strip is metallurgically very hard, where-by in both conditions thestrip lends itself to ready handling, transferring and processing withminimum losses due to breakage, bending, tearing and the like, andfurther characterized by the fact that all of the rolling processes areperformed prior to the tinning of the strip, the steps including:

cold reducing the strip to a gauge of at least .006 inch and greaterwhich will be relatively thick as compared with the desired final gaugethereof;

continuously annealing the strip while in its relatively thickcondition;

cold reducing the soft annealed relatively thick strip at least 30% andgreater to its final thin gauge to impart a substantial hardness andstrength to the strip,

and as a final step tinning the strip in its thin hard condition.

References Cited in the file of this patent UNITED STATES PATENTS2,673,836 Vouada Mar. 30, 1954 2,906,652 Kiefer Sept. 29, 1959 FOREIGNPATENTS 1520,373 Australia Sept. 27, 1945 472,120 Canada Mar. 13, 19511

1. IN A METHOD OF PRODUCING TINPLATE CHARACTERIZED BY A HIGH DEGREE OFHARDNESS SUITABLE FOR USE IN THE MANUFACTURE OF CONTAINERS, THE STEPSINCLUDING: COLD REDUCING THE STRIP TO A THICKNESS OF AT LEAST .006 INCHAND THICKER; ANNEALING SUCH STRIP; COLD REDUCING THE ANNEALED STRIP BYAN AMOUNT OF AT LEAST 30 PERCENT AND GREATER TO IMPART TO THE STRIP AJARDNESS OF AT LEAST T-5, AND ELECTROLYTICALLY TINNING THE STRIP IN ITSTHIN HARD CONDITION.